Draining the boiler

Hello,

I have a query I hope somebody can help me with. I would like to drain my combi boiler so I can take out and clean the plate heat exchanger. Firstly, do I drain from the heating return? Secondly, I can't seem to find an access point I can connect a hose to (see picture). Do I have to unscrew the hexagonal bit on the end and screw in a fitting that then will connect to a hose ?

Thanks

Sounds like you need a gas safe engineer.